Search for Heavy Majorana Neutrinos in <i>e</I><sup>±< and <i>e</I><sup>±< Final States Via Ww Scattering in <i>pp</I> Collisions at √<i>s</I>=13 Tev With the Atlas Detector

Abstract

A search for heavy Majorana neutrinos in scattering of same-sign.. boson pairs in proton-proton collisions at root s = 13 TeV at the LHC is reported. The dataset used corresponds to an integrated luminosity of 140 fb(-1), collected with the ATLAS detector during 2015-2018. The search is performed in final states including a same-sign ee or e mu pair and at least two jets with large invariant mass and a large rapidity difference. No significant excess of events with respect to the Standard Model background predictions is observed. The results are interpreted in a benchmark scenario of the Phenomenological Type-I Seesaw model. New constraints are set on the values of the vertical bar V-eN vertical bar(2) and vertical bar VeNV mu N*vertical bar parameters for heavy Majorana neutrino masses between 50 GeV and 20 TeV, where V-eN is the matrix element describing the mixing of the heavy Majorana neutrino mass eigenstate with the Standard Model neutrino of flavour l = e, mu. The sensitivity to the Weinberg operator is investigated and constraints on the effective ee and e mu Majorana neutrino masses are reported. The statistical combination of the ee and e mu channels with the previously published mu mu channel is performed.